The present disclosure generally relates to semiconductor apparatuses and manufacturing processes, and more particularly, relates to a post chemical mechanical polishing (CMP) process for use with fluorinated silicate glass.
In conventional integrated circuit fabrication, circuit elements are formed by etching a pattern of gaps in a layer of metal such as aluminum. The gaps are then filled with a dielectric such as silicon dioxide. Copper is now being used as the metal conductor for most types of integrated circuits because of its lower resistance when compared to conventional aluminum alloys. Because it is difficult to etch copper, however, damascene processes have been developed for fabricating copper-based integrated circuits. In damascene processes, dielectric layers are deposited and then etched to form gaps that are subsequently overfilled with copper. Once the copper layer is formed, the substrate subsequently undergoes a planarization process to remove conductive material above the dielectric, such as by chemical mechanical polishing. The process is repeated as necessary for each additional layer.
The low dielectric constants of fluorine-containing dielectrics such as fluorinated diamond-like-carbon, fluorinated silicon oxide, and fluorinated silicate glass, make them potentially useful as interlayer dielectric materials in high performance VLSI and ULSI chips where interconnect wiring capacitance must be minimized. Fluorine-containing dielectrics can be deposited in conventional PECVD systems, which have been widely used for undoped silicate glass and fluorine-containing dielectrics in aluminum interconnects. Fluorine-containing dielectrics generally have a good process scheme in terms of reliability, stability, and throughput. Furthermore, the electrical performance of integrated circuits can be significantly improved due to the lower dielectric constant of fluorine-containing dielectrics (about 3.4 to about 3.7 compared to about 4.1 for conventional silicon oxides). The lower dielectric constant reduces the capacitance between metal lines in the same layer and reduces cross talk across layers.
Unfortunately, the presence of fluorine-containing dielectrics in metal insulator wiring structures raises other issues. It has been found that fluorine-containing dielectrics cannot be easily integrated into these interconnect structures. For example, it has been found that fluorine in the fluorine-containing dielectric can react with copper metal conductors in presence of water and cause the copper metal conductor to redeposit and form dendrite- or nodule-like structures. The relative humidity in the fabrication environment provides sufficient amounts of moisture for this reaction to occur. While the exact mechanism is presently unknown, it is believed that an electrochemical reaction occurs that is facilitated by the presence of fluorine and water. While interlayer dielectrics with reduced fluorine contents would be expected to have smaller amounts of fluorine available to react, lower fluorine-content interlayer dielectrics have undesirably higher k values.
Current methods to overcome this phenomenon generally require a capping or liner material, or rely on time-based measurements. Capping materials such as the silicon oxide and silicon nitride insulators, and the conductive liner materials such as TiN have previously been described for use with fluorine-free interlayer dielectrics as (i) diffusion barriers (to prevent atoms of wiring material from diffusing into the interlayer dielectric, from where they may readily diffuse into active device regions), (ii) etch stop and permanent masking materials, and (iii) adhesion layers.
With regard to time-based measurements, once a predetermined period of time has expired, the substrate must be treated to remove the corrosion of the conductors, such as by chemical mechanical polishing. The predetermined periods of time before corrosion occurs is relatively short and as such, time based measurements are generally not a practical solution.
Accordingly, there remains a need to prevent corrosion of metal conductors in contact with fluorine-containing dielectrics as well as prevent the formation of dendritic or nodule-like structures.